1. Field of the Invention
The present invention relates to a nonaqueous electrolytic solution with improved safety and a lithium battery employing the same, and more particularly, to a nonaqueous electrolytic solution with improved safety when the battery is overcharged, and a lithium battery employing the polymer electrolyte.
2. Description of the Related Art
A lithium battery includes a cathode, an anode and an electrolytic solution providing a movement path of lithium ions between the cathode and the anode, and generates electric energy by oxidation and reduction when the lithium ions are intercalated into/deintercalated from the cathode and anode.
When a battery is overcharged due to, for example, malfunction of a charger, resulting in a rapid increase in voltage, excessive lithium is extracted from the cathode with a corresponding excessive insertion of lithium at the anode, thermally destabilizing both the cathode and the anodes. As a result, an organic solvent contained in the electrolytic solution is decomposed and a rapid exothermic reaction occurs, leading to thermal runaway, which severely impairs safety of the battery.
To overcome these problems, a method of adding additives to the electrolytic solution has been proposed.
For example, U.S. Pat. No. 5,709,968 discloses that thermal runaway occurring due to overcharge current is prevented by adding a benzene compound such as p-chloroanisole to an electrolytic solution. U.S. Pat. No. 5,879,834 discloses that aromatic additives such as biphenyl, 3-chlorothiophene, and furan are added to an electrolytic solution, and such additives are electrochemically polymerized at abnormally high voltages, thus increasing the internal resistance of a battery and protecting the battery.
However, according to the above-described methods, compounds added as additives may be electrochemically polymerized at normal operating conditions of a battery or generate a large amount of gas due to oxidative decomposition, so that swelling of the battery may increase, and battery performance such as a high-rate characteristic or a life characteristic may be decreased, making it difficult to put the batteries manufactured by the methods into practice.